World War II began in 1939 after Germany invaded Poland. Key events leading up to the war included the rise of nationalist dictators like Hitler in Germany, Mussolini in Italy, and Stalin in the Soviet Union. These totalitarian leaders exploited economic instability and popular discontent following World War I and the Great Depression to consolidate power. Hitler steadily expanded German territory through the late 1930s, and the failed policy of appeasement by Britain and France emboldened Germany and led to the invasion of Poland and start of World War II.